Move2SD moves parts of the apps to the EXTERNAL microSD card for me. IT will be kept in the android_secure folder which you can view and browse via PC when connected as USB mass storage.
Small apps like Angry Birds (20MB) or Where's My Water (45MB) are stored fully in the 1.9GB internal memory. You can move around 90% or so of that into the external microSD.
The USB storage is for your use to store music, documents, etc. Big games will have their data here as well. For example Fifa12 where 1.2GB will be kept in the USB storage and only say 10MB in the internal memory. Move2SD will only move that 10MB and will not touch the 1.2GB which can't be moved unless rooted.
SO to clear your internal memory, use move2SD. Go to Settings/Manage Applications and under the On SD tab, you can tap on any app and choose to move2SD. Any app with the tick beside it is already in the microSD.